Demo Update - Walljumping, sliding, tutorial, firing range, and more.

Worked on the demo some more, apologies for the long delay.

Additions include:

-Tutorial mission

-Walljumping for a speed boost

-Sliding to preserve momentum

-Tweaked enemy AI, they should be more aggressive now

-Reimplemented remote demolition charges in place of the frag grenades

-Adjusted weapon balance

-Adjusted map flow and geometry- there's an alternate path in the first mission from the bottom area now

-Leaning is more useful now

-Firing range added after completing the demo

-UI tweaks

-Added options to invert mouse aim on individual axis

-Accessibility options to add a reference crosshair in the center of the screen and adjust screenshake

-You can use the mouse wheel to scroll through weapons now

-Adjusted heartbeat sensor mechanics, now only visible in reflex mode, where they're always visible.

-Tweaked particle effects

And some other minor fixes. Thanks for taking the time to play my game!